Today's children are the “least active generation in history” and could be the first to have a shorter life expectancy than their parents, former Olympic champion Lord Coe has warned.

Writing in The Telegraph he urged families, schools and businesses to take action to tackle sedentary lifestyles which are causing thousands of premature deaths and costing the UK economy £20bn each year.

The appeal comes as a report from an All Party Commission on Physical Activity calls for radical changes to “turn back the toxic tide of inactivity” - including altering the way schools are run, to ensure that children take more exercise.

It says schools should open “breakfast fitness clubs” so that pupils get exercise before the day starts, with extra activity sessions scheduled between lessons, or during them.

The report shows that just half of seven-year olds are meeting Government recommendations to have an hour’s moderate to vigorous physical activity each day, with levels of activity halving again between the age of nine and 15.

Lord Coe, who was chairman of the London Organising Committee for the Olympic Games, writes: “Today’s children are the least active generation in history.

"They also might be the first generation to have a shorter life expectancy than their parents. That’s not progress, that’s moving backwards, and physical inactivity may be a bigger culprit than we think.”

The All Party Commission on Physical Activity warned that over half of all adults do not get the minimum amount of exercise recommended by experts.

The report by MPs warns that fewer children are playing freely in streets, parks and open spaces, with many ferried to school by car by parents who spend most of their working lives behind a desk.

It highlights research which shows the average office worker now spends five hours 41 minutes sitting at their desk each day, while just 22 per cent of adults achieve even half an hour’s exercise a week.

The commission says the average Briton is 24 per cent less active than in 1961, and on course to be 35 per cent less active by 2030, with the lack of activity linked to a rising burden of ill-health, from conditions such as type 2 diabetes, heart disease and cancer.

It states: “Physical inactivity leads to around 37,000 premature deaths a year - a number that is more than all deaths from murder, suicide and accident combined. Lack of physical activity is estimated to double the rate of absenteeism at work, and to cost the UK economy billions every year.”

In the report, MPs call for changes in town and transport planning in order to make it easier for people to make more journeys on foot or by bicycle.

Malcolm Shepherd, chief executive of charity Sustrans said: “The easiest and single most effective way of increasing physical activity is to transform our daily journeys to school, work or leisure into active journeys by walking or cycling. The average primary school journey is just 1.5 miles – the perfect distance to walk or cycle. If eight out of ten primary school journeys were made by bike or on foot, many of our physical activity ambitions would be realized."